Battery Charging System

ABSTRACT

There is provided a planar inductive battery charging system designed to enable electronic devices to be recharged. The system includes a planar charging module having a charging surface on which a device to be recharged is placed. Within the charging module and parallel to the charging surface is at least one and preferably an array of primary windings that couple energy inductively to a secondary winding formed in the device to be recharged. The invention also provides secondary modules that allow the system to be used with conventional electronic devices not formed with secondary windings.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/269,936, filed Oct. 10, 2011, now issued as U.S. Pat. No. ______,which application is a continuation-in-part of U.S. patent applicationSer. No. 12/950,814, filed Nov. 19, 2010, now issued as U.S. Pat. No.8,269,456, which is a continuation of co-pending U.S. patent applicationSer. No. 12/486,572, filed Jun. 17, 2009, now issued as U.S. Pat. No.7,872,445, entitled “RECHARGEABLE BATTERY POWERED PORTABLE ELECTRONICDEVICE,” which is a continuation of U.S. patent application Ser. No.11/610,860, filed Dec. 14, 2006, now issued as U.S. Pat. No. 7,576,514,entitled “PLANAR INDUCTIVE BATTERY CHARGING SYSTEM” (as amended), whichis a continuation of U.S. patent application Ser. No. 11/009,478, filedDec. 10, 2004, now issued as U.S. Pat. No. 7,164,255, entitled“INDUCTIVE BATTERY CHARGER SYSTEM WITH PRIMARY TRANSFORMER WINDINGSFORMED IN A MULTI-LAYER STRUCTURE” (as amended), which is a continuationof PCT International Application PCT/AU2003/000721, filed Jun. 10, 2003,and published under PCT Article 21(2) in English as WO 03/105308 on Dec.18, 2003. PCT/AU2003/000721 claimed benefit from British ApplicationsGB0213374.2, filed on Jun. 10, 2002; GB0226893.6, filed on Nov. 18,2002; and GB0305428.5, filed on Mar. 10, 2003. Accordingly, priority forthis continuation application is claimed from British ApplicationNumbers GB0213374.2, GB0226893.6, and GB0305428.5. The disclosures ofeach of the prior related applications are incorporated herein byreference in their entirety.

TECHNICAL FIELD

This invention relates to a battery charger, and in particular to abattery charger having a planar surface on which one or more batterypowered devices may be placed for battery recharging through induction.The invention also extends to a battery charging system for use withconventional electronic devices and that allows conventional electronicdevices to be charged using the battery charging system of the presentinvention.

BACKGROUND

Portable electronic equipment such as mobile phones, handheld computers,personal data assistants, and devices such as a wireless computer mouse,are normally powered by batteries. In many cases, rechargeable batteriesare preferred because of environmental and economical concerns. The mostcommon way to charge rechargeable batteries is to use a conventionalcharger, which normally consists of an AC-DC power supply (in case ofusing the ac mains) or a DC-DC power supply (in case of using a carbattery). Conventional chargers normally use a cord (an electric cablefor a physical electrical connection) to connect the charger circuit (apower supply) to the battery located in the portable electronicequipment. The basic schematic of the conventional battery charger isshown in FIG. 1.

Inductive electronic chargers without direct physical electricalconnection have been developed in some portable electronic equipmentsuch as electric toothbrushes where because they are designed to be usedin the bathroom in the vicinity of sinks and water, it is not safe toprovide a conventional electrical connection. Various known inductivetype chargers, however, use traditional transformer designs withwindings wound around ferrite magnetic cores as shown in FIG. 2. Themain magnetic flux between the primary winding and secondary winding hasto go through the magnetic core materials. Other contactless chargersproposed also use magnetic cores as the main structure for the coupledtransformer windings.

A contactless charger using a single primary printed winding without anyEMI shielding has been proposed for portabletelecommunications/computing electronics. However, the magnetic fluxdistribution of a single spiral winding has a major problem ofnon-uniform magnetic flux distribution. As illustrated further below,the magnitude of the magnetic field in the centre of the core of aspiral winding is highest and decreases from the centre. This means thatif the portable electronic device is not placed properly in the centralregion, the charging effect is not effective in this non-uniform fielddistribution. Furthermore, without proper EMI shielding, undesirableinduced currents may flow in other metallic parts of the portableelectronic equipment.

SUMMARY OF THE INVENTION

According to the present invention there is provided a charging modulefor a battery charging system, said module comprising a charging circuitand a charging surface for receiving a secondary module for charging anelectronic device, wherein said charging module comprises a transformerprimary winding substantially parallel to said charging surface, andsaid charging circuit is separate to said charging surface.

In a preferred embodiment the primary winding is formed on a planarprinted circuit board.

Preferably the magnetic flux generated by the primary winding issubstantially uniform over at least a major part of the planar chargingsurface. In this way the precise position and orientation of theelectronic device on the charging surface is not critical. To achievethis the charging module may comprise a plurality of primary windings,which may preferably be disposed in a regular array.

In a preferred embodiment the primary winding is provided withelectromagnetic shielding on the side of said winding opposite from saidplanar charging surface. This shielding may include a sheet of ferritematerial, and more preferably also may further include a sheet ofconductive material such as copper or aluminum.

It is an advantage of the present invention that in preferredembodiments the planar charging surface may be large enough to receivetwo or more electronic devices, and the primary charging circuit isadapted to charge two or more devices simultaneously. In this way it ispossible to charge more than one device simultaneously. For example theplanar charging surface may be divided into a plurality of chargingregions, which regions may be defined by providing a plurality ofprimary transformer windings arranged in a regular array and connectingthe windings in groups to define said charging regions. A furtheradvantage of the present invention is that it enables the possibility ofallowing a device to move over the charging surface while being chargedat the same time. This possibility is particularly useful to a devicewhich is designed to be moved such as a wireless computer mouse

Viewed from another aspect the present invention provides a batterycharging system comprising a charging module comprising a primarycharging circuit and being formed with a charging surface for receivingan electronic device to be charged, wherein said charging modulecomprises a plurality of transformer primary windings arranged in aregular array.

In addition to the battery charging system, the invention also extendsto a battery powered portable electronic device comprising arechargeable battery, and wherein the device includes a planar secondarywinding for receiving electrical energy from a battery charger, andelectromagnetic shielding between the winding and the major electroniccomponents of said device.

Preferably the shielding comprises a sheet of ferrite material and asheet of conductive material such as copper.

Preferably the winding is formed integrally with a back cover of saiddevice.

An important aspect of the present invention is that it provides abattery charging system that employs a localized charging concept. Inparticular, when there is an array of primary coils, it will beunderstood that energy is only transferred from those primary coils thatare adjacent the secondary coil located in the device being charged. Inother words, when a device is placed on a planar charging surface thatis greater in size than the device, energy is only transferred from thatpart of the planar charging surface that is directly beneath the device,and possibly also immediately adjacent areas that are still able tocouple to the secondary coil.

Viewed from another aspect the present invention provides a batterycharging system comprising a primary module and at least one secondarymodule, said primary module comprising means for connecting to a mainssupply, and at least one primary winding adjacent to a charging surfaceof said primary module, and wherein said secondary module comprises asecondary winding adjacent to a surface of said secondary module,circuit means for converting alternating current generated in saidsecondary winding to a regulated DC output, and a charging connector forconnection to the charging socket of an electronic device.

According to another aspect the invention also extends to a secondarymodule for a battery charging system, comprising: a housing having atleast one charging surface, a winding provided in said housing adjacentto said surface and adapted to receive magnetic flux when said surfaceis brought adjacent to a primary winding, circuit means for convertingalternating current in said secondary winding to a regulated DC output,and a connector means for connecting said DC output to the chargingsocket of an electronic device.

BRIEF DESCRIPTION OF THE DRAWINGS

Some embodiments of the invention will now be described by way ofexample and with reference to the accompanying drawings, in which:

FIG. 1 is a schematic view of a conventional prior art battery chargerwith direct electrical connection;

FIG. 2 is a schematic view of a conventional magnetic core-basedtransformer as used in prior art inductive battery charger systems;

FIG. 3 is a schematic view of a planar transformer with shielding;

FIGS. 4( a)-(c) are (a) a perspective view of a battery charger systemaccording to an embodiment of the present invention, (b) a view similarto (a) but showing the structure of the primary charging system, and (c)a view similar to (a) and (b) but showing the top cover removed forclarity;

FIGS. 5( a) & (b) show the structure of the primary charger with the topcover removed for clarity, and in FIG. 5( a) with the structure shown inexploded view;

FIGS. 6( a) & (b) show (a) a single spiral PCB winding, and (b) themeasured magnetic field distribution of a single spiral winding;

FIGS. 7( a) & (b) illustrate the use of a magnetic core to controlmagnetic field distribution;

FIG. 8 shows an embodiment of the invention in which a plurality ofprimary windings are arranged in an array structure;

FIGS. 9( a) & (b) shows (a) a 4×4 primary winding array, and (b) theresulting magnetic field distribution;

FIGS. 10( a)-(c) illustrate an embodiment of the invention in whichprimary windings are arranged in groups with FIG. 10( c) showing theequivalent circuit;

FIG. 11 shows an example of the back cover of an electronic devicedesigned to be recharged using an embodiment of the present invention;

FIGS. 12( a)-(d) show exploded views of the back cover of FIG. 11;

FIGS. 13( a) & (b) show views of a watch that may be recharged inaccordance with an embodiment of the invention;

FIG. 14 shows a charging module in accordance with an alternativeembodiment of the invention,

FIG. 15 shows a first layer of a 4×5 winding array for use in amulti-layer embodiment;

FIG. 16 shows a second layer of a 3×4 winding array for use inconjunction with the layer of FIG. 15 in a multi-layer embodiment,

FIG. 17 shows the layers of FIG. 15 and FIG. 16 in the two-layerstructure;

FIG. 18 is simplified version of FIG. 15;

FIG. 19 is a simplified version of FIG. 16;

FIG. 20 is a simplified version of FIG. 17;

FIG. 21 is a plot showing the smoothing effect of the two-layerstructure;

FIG. 22 shows a hexagonal spiral winding;

FIG. 23 is a simplified form of FIG. 22;

FIG. 24 shows a single-layer of hexagonal spiral windings;

FIG. 25 shows two adjacent hexagonal spiral windings;

FIG. 26 shows the mmf distribution of the adjacent windings of FIG. 25;

FIG. 27 shows three adjacent hexagonal spiral windings and the peaks andminima of the flux distribution;

FIG. 28 shows two overlapped layers of hexagonal spiral windings;

FIG. 29 shows the location of the peak flux in the structure of FIG. 28;

FIG. 30 corresponds to FIG. 29 but also shows the location of the fluxminima;

FIG. 31 shows an embodiment of the invention formed with threeoverlapped layers;

FIG. 32 corresponds to FIG. 31 but shows the location of the flux peaks;

FIG. 33 is a plot showing the uniformity of the flux distribution alonga line;

FIG. 34 shows a square spiral winding;

FIG. 35 is a simplified version of FIG. 34;

FIG. 36 shows a first layer of square spiral windings;

FIG. 37 corresponds to FIG. 36 but shows the location of the flux maximaand minima;

FIG. 38 shows two overlapped layers of square spiral windings includingthe location of the flux maxima and minima;

FIG. 39 shows three overlapped layers of square spiral windingsincluding the location of the flux maxima and minima;

FIG. 40 shows four overlapped layers of square spiral windings includingthe location of the flux maxima and minima;

FIG. 41 illustrates a battery charging system according to a furtherembodiment of the invention;

FIG. 42 is a view similar to FIG. 41 but part broken away to show theprimary winding;

FIG. 43 is a view similar to FIG. 42 but of an alternate embodiment;

FIGS. 44( a) and (b) illustrate possible magnetic cores for use in theembodiment of FIG. 42;

FIG. 45 shows an equivalent circuit for the charging system of anembodiment of the invention;

FIG. 46 illustrates an example of a secondary module for use in anembodiment of the invention;

FIG. 47 shows a part broken away view of secondary module of anembodiment of the invention;

FIG. 48 is a view similar to FIG. 47 but of a further embodiment;

FIG. 49 is a view showing the complete charging system according to anembodiment of the invention; and

FIG. 50 is a view similar to FIG. 49 but showing how the charging systemaccording to an embodiment of the invention can be used to chargemultiple devices having different forms of charging connections; and

FIG. 51 is a view illustrating how an embodiment of the presentinvention can be used to enable a conventional electronic device to becharged using an inductive charging platform as shown in FIG. 4.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention will now be described in respect of a preferredembodiment in the form of an inductive battery charger for portableelectronic equipment such as mobile phones, handheld computers andpersonal digital assistants (PDA), and devices such as a wirelesscomputer mouse.

Referring firstly to FIG. 4, the inductive charger system comprises twomodules, a power delivering charger module that contains the primarycircuit of a planar isolation transformer and a secondary circuit thatis located in the portable electronic equipment to be charged. In thisembodiment of the invention, the charger circuit is located within ahousing 1 that is formed with a flat charging surface 2. The secondarycircuit is formed in the portable equipment to be charged (in thisexample a mobile phone 3) and the equipment is formed with at least oneplanar surface. As will be seen from the following description theequipment is charged simply by placing the equipment on the surface sothat the planar surface on the equipment is brought into contact withthe flat charging surface 2. It is a particularly preferred aspect ofthe present invention that the equipment to be charged does not have tobe positioned on the charging surface in any special orientation.Furthermore, in preferred embodiments of the invention two or moremobile devices may be charged simultaneously on the same chargingsurface, and in another embodiment, a device that is designed to bemoved (such as a wireless computer mouse) can be charged while beingmoved over the charging surface (which could be integrated into acomputer mouse pad). It will also be seen from the following descriptionthat the energy transfer is localized in the sense that energy is onlytransferred from the charging surface to the device from that part ofthe charging surface that is directly beneath the device (and possiblyto a lesser extent regions adjacent thereto).

Referring in particular to FIG. 4( b) the primary charging modulecomprises a printed circuit board 4 formed with at least one spiralconductive track formed thereon as a primary winding. It will beunderstood, however, that the primary winding need not necessarily beformed on a PCB and could be formed separately. Alternatively, multiplePCBs each formed with at least one winding could be “stacked” on top ofeach other to increase the total flux. Preferably, as will be describedfurther below, there are in fact a plurality of such spiral tracksdisposed in an array as shown in FIG. 4( c) in which a top insulatingsheet has been removed for clarity. Beneath the PCB 4 (i.e., the side ofthe PCB away from the charging surface) is provided EMI shieldingcomprising firstly a ferrite sheet 5 adjacent the PCB 4, and then aconductive sheet 6 which in this example may be a copper sheet. Beneaththe copper sheet 6 may be provided any suitable form of substratematerial 7, e.g., a plastics material. Above the PCB 4 may be provided asheet of insulating material 8 which forms the charging surface.Preferably the PCB 4, the EMI shielding sheets 5,6, the substrate 7 andthe insulating cover sheet 8 may also be generally the same size andshape, for example rectangular, so as to form the primary chargingmodule with the charging surface being large enough to accommodate atleast one, and more preferably two or more, devices to be charged. FIGS.5( a) and (b) also show the structure of the charging module without thecover sheet and without any devices to be charged thereon for the sakeof clarity.

As shown in FIG. 4, the primary transformer circuit module transmitselectrical energy at high frequency through a flat charging surface thatcontains the primary transformer windings. The secondary winding is alsoplanar and is located in the portable electronic equipment and couplesthis energy, and a rectifier within the portable equipment rectifies thehigh-frequency secondary AC voltage into a DC voltage for charging thebattery inside the portable equipment either directly or via a chargingcircuit. The rectified DC voltage is applied to the battery viamechanical contacts provided in an integrated back cover as will bedescribed further below. No physical electrical connection between theprimary charger circuit and the portable electronic equipment is needed.

The primary charger circuit has (1) a switched mode power electroniccircuit, (2) the primary side of a planar transformer that consists of agroup of primary windings connected in series or in parallel or acombination of both, (3) an EMI shield and (4) a flat interface surfaceon which one or more portable electronic devices can be placed andcharged simultaneously. The schematic of the primary charger system isshown in FIGS. 5( a) and (b) without the insulating cover.

The battery charging system can be powered by AC or DC power sources. Ifthe power supply is the AC mains, the switched mode power electroniccircuit should perform a low-frequency (50 or 60 Hz) AC to DC powerconversion and then DC to high-frequency (typically in the range from 20kHz to 10 MHz) AC power conversion. This high-frequency AC voltage willfeed the primary planar windings of the primary charger circuit. If thepower supply is a battery (e.g., a car battery), the switched mode powersupply should perform a DC to high-frequency AC power conversion. Thehigh-frequency voltage is fed to the primary windings of the planartransformer.

Preferably, the charger should be able to charge one or more than oneitems of portable electronic equipment at the same time. In order toachieve such a function, the AC magnetic flux experienced by each itemof portable equipment placed on the charging surface should be as evenas possible. A standard planar spiral winding as shown in FIG. 6( a) isnot suitable to meet this requirement because its flux distribution isnot uniform as shown in FIG. 6(b) when the winding is excited by an ACpower source. The reason for such non-uniform magnetic flux distributionis that the number of turns in the central region of the single spiralwinding is largest. As the magnitude of the magnetic flux and themagnetomotive force (mmf) is proportional to the product of the numberof turn and the current in the winding, the magnetic flux is highest inthe center of the winding.

One method to ensure uniform magnetic flux or mmf distribution is to usea concentric primary winding with a planar magnetic core as shown inFIG. 7( a). This magnetic core-based approach allows the magnetic fluxto concentrate inside the core and typical magnetic flux distribution isshown in FIG. 7( b). In general, the flat charging interface surface ofthe primary charger should be larger than the total area of the portableelectronic equipment.

In order to ensure that more than one item of portable electronicequipment can be placed on the flat charging surface and chargedsimultaneously, a second and more preferred method proposed is to ensurethat the magnetic flux distribution experienced by each items ofportable electronic equipment is as uniform as possible. This method canbe realized by using a “distributed” primary planar transformer windingarray structure as shown in FIG. 8. This planar winding array consistsof many printed spiral windings formed on the PCB. These printed spiralwindings can be hexagonal, circular, square or rectangular spirals, andcan be connected in series, in parallel or a combination of both to thehigh-frequency AC voltage generated in the power supply in the primarycharger circuit. The array comprises relatively closely spaced coils soas to be able to generate the required near-uniform magnetic fluxdistribution, as an array of widely spaced apart coils may not generatesuch a near-uniform field.

FIG. 9( a) shows a practical example with the transformer winding arrayconnected in series so that all the fluxes created in the windings pointto the same direction. FIG. 9(b) show the measured flux distribution ofone planar transformer when the windings in the transformer array areconnected in series. This measurement confirms the near uniform magneticflux distribution of the array structure. Comparison of FIG. 6( b) andFIG. 9( b) confirms the improvement of the uniform magnetic fielddistribution using the transformer array structure. In addition, thistransformer array structure provides for the possibility of multipleprimary transformer windings being provided for localized charging aswill now be explained.

The primary transformer windings can also take the form of a combinationof series and parallel connections if desired. Such an arrangementallows the charging surface to be divided into various charging regionsto cater for different sizes of the secondary windings inside theportable electronic equipment. FIG. 10( a) illustrates this localizedcharging zone principle. Assume that the transformer array is dividedinto 4 zones (A, B, C, and D). The transformer windings within each zoneare connected in series to form one primary winding group with thedistributed magnetic flux feature. There will be four primary windingsin the equivalent circuit as shown in FIG. 10( c). If the portableelectronic equipment is placed on Zones A and B as shown in FIG. 10( b),the equivalent electrical circuit is shown in FIG. 10( c). Only theparallel primary transformer winding groups for Zones A and B are loadedbecause they can sense a nearby secondary winding circuit in theportable electronic equipment. Therefore, they will generate magneticflux in Zones A and B. Primary transformer windings C and D are notloaded because they have no secondary transformer circuit close to themand their equivalent secondary circuits are simply an open-circuit (FIG.10( c)). As a result, power transfer between the primary charger circuitand the secondary windings inside the portable electronic equipmenttakes place basically through the coupled regions (areas) of thecharging interface surface covered by the portable electronic equipment.The non-covered area of the charging surface will transfer virtually noenergy. This special design avoids unnecessary electromagneticinterference. A further advantage of this localized energy transferconcept, is that it enables a movable device (such as a wirelesscomputer mouse) to be continually charged as it moves over the chargingsurface. In the case of a wireless computer mouse, for example, theprimary charging circuit could be integrated into a mouse pad and themouse may be charged as it rests on or moves over the mouse pad.

The back cover of the portable electronic equipment is a detachable backcover shown in FIG. 12( a) that covers the battery and which may beremoved when the battery is replaced. In preferred embodiments of thepresent invention, this back cover has a built-in secondary planartransformer winding 10, a diode rectifier circuit 13 and preferably athin EMI shield 11, 12 as shown in FIGS. 12( b) and 12(c). When the backcover side of the portable equipment is placed near the flat chargingsurface of the primary charger circuit, this secondary winding couplesthe energy from the nearby primary transformer winding or windings. Therectifier circuit rectifies the coupled AC voltage into a DC voltage forcharging the battery through mechanical contacts 14. This rectifiercircuit also prevents the battery from discharging into the secondarywinding. In order to avoid induced circuit from circulating in othermetal parts inside portable electronic circuit, it is preferable toinclude a thin EMI shield as part of the integrated back cover structureas shown in FIG. 12. This EMI shield can be a thin piece of ferritematerial (such as a flexible ferrite sheet developed by Siemens) orferrite sheets, or more preferably a combination of a ferrite sheet 11and then a thin sheet 12 of copper of another conductive material suchas aluminum.

It will thus be seen that, at least in its preferred forms, the presentinvention provides a new planar inductive battery charger for portableelectronic equipment such as mobile phones, handheld computers, personaldata assistant (PDA) and electronic watches, and wireless computer mice.The inductive charger system consists of two modules, including (1) apower delivering charger circuit that contains the primary circuit of aplanar isolation transformer and a flat charging surface and (2) aseparate secondary transformer circuit that consists of a printedwinding, a rectifier and preferably a thin EMI shield and which islocated in the portable electronic equipment to be charged.

An advantage of the present invention, at least in preferred forms, isthat the primary charger circuit system has the primary side of a planartransformer and a flat interface surface on which one or more portableelectronic devices can be placed and charged simultaneously. Thesecondary circuit can be integrated into the back cover of the portableelectronic device or separately placed inside the electronic device. Theinvention also extends to a back cover design with an in-built secondarycircuit for the portable equipment. The secondary winding of the planartransformer can be EMI shielded and integrated into the back coveradjacent to the battery in the portable electronic device. As long asthe back cover sides of the portable electronic device are placed on thecharger surface, one or more portable electronic devices can be chargedsimultaneously, regardless of their orientations.

FIGS. 13( a) and (b) show how an embodiment of the invention may be usedto recharge a watch battery. A watch is formed with a basic watchmechanism 20, which is powered by a rechargeable battery 21. The watchmechanism is shielded from electrical interference in the chargingprocess by an EMI shield consisting of, for example, a copper sheet 22and a ferrite sheet 23 (with the copper sheet closer to the watchmechanism than the ferrite sheet). The other side of the EMI shield isprovided a planar coreless transformer secondary winding 24 formed withelectrical contacts 26 for connection to the battery 21 and with arectifier circuit to prevent discharge of the battery. Finally, thewatch structure is completed by the provision of a planar back cover 25formed of non-metallic material. It will be understood that the watchbattery may be recharged by placing the watch on the charging surface ofa battery charging system as described in the above embodiments suchthat the back cover 25 lies flat on the planar charging surface.Electrical energy is then coupled from the primary winding(s) in thebattery charging module to the secondary winding in the watch and thento the rechargeable battery.

In the embodiments described above the charging module is formed as asingle integral unit (as shown for example in FIGS. 4 and 5). However,in some situations it may be desirable to separate the electroniccharging circuit from the planar charging surface. This possibility isshown in FIG. 14 in which the electronic charging circuit 30 isconnected by a cable 31 to the charging surface 32. It must be notedthat in some embodiments the cable 31 is very short so that theelectronic charging circuit 30 and the charging surface 32 are veryclose or attached to each other but are still in two separate units. Theelectronic charging circuit 30 can also be integrated into an AC/DCadaptor with the charging module being powered by an AC power sourcethrough the AC/DC adaptor, or be integrated with other electroniccircuits if the charging module is a part of a larger system. Thecharging surface 32 includes an insulating top cover, the planar primarywindings printed on a PCB, and a bottom EMI shield formed of ferrite anda conductive sheet such as copper. This embodiment has the advantagethat the charging surface is relatively thin, and therefore may beuseful for example when the device to be charged is a wireless computermouse because the charging surface can double as a mouse pad as well asa charging surface. These embodiments where the charging circuit 30 andthe charging surface 32 are separate have several advantages. Inembodiments with the electronic charging circuit and the chargingsurface being sufficiently separated and/or having good thermalinsulation between each other, there is the advantage of good thermalmanagement since the heat generated from the power loss in theelectronic charging circuit 30 has less impact to the charging surface32 and the device being charged on the charging surface. In embodimentswith the electronic charging circuit and the charging surface beingseparated and/or having good electromagnetic insulation between eachother, there is the advantage that the radio frequency interference fromthe electronic charging circuit 30 to the charging surface 32 and thedevice being charged on the charging surface is less.

In the embodiments described above a single layer of transformer arraysis provided. However, in order to generate a more uniform magnetic fielddistribution, multi-layer transformer arrays can be used. The followingembodiments describe how multiple layers of transformer arrays may beused that can provide a very uniform magnetic field distribution on thecharging surface.

FIG. 15 shows a 4×5 primary planar transformer winding array whichconsists of square-spiral winding patterns. This can be fabricated onone layer of the printed circuit board structure. It should be notedthat, for an individual winding pattern in the array, the magnitude ofthe magnetic flux is highest in the center of the spiral winding. Themagnitude of the magnetic flux is smallest in the small gap betweenadjacent winding patterns.

A second layer with a 3×4 transformer winding array is shown in FIG. 16.The individual winding patterns in both layers are identical. As shownin FIG. 17, by having the two layers of arrays arranged in such a mannerthat the center (region of maximum magnetic flux magnitude) of a windingpattern on one layer is placed on the gap (region of minimum magneticflux magnitude) between adjacent winding patterns on the other layer,the variation of the magnetic field magnitude can be minimized and themagnetic flux magnitude can therefore be made as even as possible overthe overlapped surface. The essence of the multi-layer transformerarrays is to have a displacement between the individual winding patternsof the two layers so that the regions of the maximum magnetic fieldmagnitude of one layer are superimposed on the regions of the minimummagnetic field magnitude of the other layer.

In order to examine the ‘uniform magnetic field magnitude’ feature ofthe proposed overlapped multi-layer transformer arrays, this ‘magnitudesmoothing’ concept is illustrated in simplified diagrams in FIGS. 18 to20. FIG. 18 is a simplified version of FIG. 15. Each solid square inFIG. 18 represents a square-spiral winding pattern in the first layer(FIG. 15). FIG. 19 is a simplified version of the FIG. 16. Each dottedsquare represents a square-spiral winding pattern in the second layer(FIG. 16). The simplified version of the multi-layer array structure isshown in FIG. 20. From FIG. 20, it can be seen that the overlapped arraystructure (with correct displacement between the two layers) divideseach square-spiral winding pattern into four smaller sub-regions. Theimportant feature is that the four sub-regions are identical in terms ofwinding structure. Despite that fact that the distribution of themagnetic field magnitude on the surface of each individual square-spiralwinding is not uniform, the distribution of the resultant magnitudefield magnitude on the surface of each sub-region is more or lessidentical because of the overlapped multi-layer winding structure. Theconcept of the generating uniform magnetic field magnitude over thecharging surface is illustrated in FIG. 21.

In this example, a multi-layer transformer winding array structure thatcan provide a uniform magnetic field magnitude distribution isdescribed. This example is based on square-spiral winding patterns. Inprinciple, winding patterns of other shapes can also be applied as longas the resultant magnetic field magnitude distribution is as uniform aspossible.

The use of two layers of transformer arrays can reduce the variation inthe magnetic flux over the charging surface. However, there may still besome variations and the use of a three or four layer structure mayprovide a still more uniform flux distribution as described in thefollowing embodiments.

The following embodiment is a structure comprising three layers ofplanar winding arrays. This PCB winding structure can generatemagnetomotive force (mmf) of substantially even magnitude over thecharging surface. Each winding array consists of a plurality spiralwindings each of which are of an hexagonal shape. A spiral windingarranged in a hexagonal shape is shown in FIG. 22. For simplicity, itwill be represented as a hexagon as shown in FIG. 23. A plurality ofhexagonal spiral windings can be arranged as an array as shown in FIG.24. These windings can be connected in parallel, in series or acombination of both to the electronic driving circuit. If a currentpasses through each spiral winding pattern, a magnetomotive force (mmf),which is equal to the product of the number of turns (N) and current (I)(i.e., NI), is generated. FIG. 25 shows two spiral winding patternsadjacent to each other and the per-unit mmf plot over the distance(dotted line) can be linearized as shown in FIG. 26. It can be seen thatthe mmf distribution over the distance is not uniform. The maximum mmfoccurs in the center of the hexagonal pattern and the minimum mmf occursin the edge of the pattern.

FIG. 27 shows three adjacent windings. The maximum mmf region is labeledby a symbol ‘P’ (which stands for Peak mmf). The minimum mmf region atthe junction of two patterns is labeled as ‘V’ (which stands for Valleyof the mmf distribution). In order to generate a uniform mmfdistribution over the planar charging surface, two more layers of PCBwinding arrays should be added. This principle is explained firstly byadding a second layer of PCB winding array to the first one as shown inFIG. 28. The second layer is placed on the first one in such a way thatthe peak mmf positions (P) of the patterns of one layer are placeddirectly over the valley positions (V) of the patterns in the otherlayer. FIG. 29 highlights the peak positions of the patterns that aredirectly over the valley positions of the other layer for the twooverlapped PCB layers in FIG. 28.

It can be observed from FIG. 29, however, that the use of two layers ofPCB winding arrays, while presenting an improvement over a single layer,does not offer the optimal solution for generating uniform mmf over theinductive charging surface. For each hexagonal pattern in the 2-layerstructure, the peak positions occupy the central position and three (outof six) vertices of each hexagon. The remaining three vertices arevalley positions (V) that need to be filled by a third layer of PCBwinding arrays. These valley positions are shown in FIG. 30 as emptysquares.

Careful examination of FIG. 30 shows that there are six peak positions(P) surrounding each valley position. Therefore, a third layer of ahexagonal PCB winding array can be used to fill up all these remainingvalley positions. By placing the central positions (peak mmf positions)of the hexagonal winding patterns of the third layer of the PCB windingarray over the remaining valley positions of the two-layer structure, anoptimal three-layer structure is formed as shown in FIG. 31. FIG. 32highlights the peak mmf positions of the three-layer structure. It canbe observed that all central positions and vertices of all hexagonalpatterns have peak mini.

In order to confirm that the mmf over the surface has uniform mmfdistribution, any distance between any two adjacent peak mmf positionscan be considered as illustrated in FIG. 33. If the winding patterns areexcited in the same manner and polarity so that the mmf generated byeach layer of the winding array are always in the same direction at anymoment, the resultant mmf is simply the sum of the mmf generated by eachlayer. The dotted line in FIG. 33 shows that the resultant mmf over thedistance between any two adjacent peak positions in FIG. 33 is equal to1.0 per unit. This confirms that the proposed three-layer PCB windingarray structure can be used to generate highly uniform mmf over theinductive charging surface. When used as a contactless, inductivecharging surface, this uniform mmf distribution feature ensures that,for a given air gap, a secondary PCB coupling winding can always couplethe same amount of magnetic flux regardless of the position of thesecondary (coupling) PCB on the inductive charging surface. In addition,the voltage induced in the secondary winding would be the same over theinductive charging surface.

In another embodiment, the three-layer PCB winding array structure canbe constructed as a four-layer PCB, with one of the four layersaccommodating the return paths of the spiral windings to the electronicdriving circuit.

A further embodiment is based again on square spiral winding patterns.In this embodiment four layers of square-spiral winding arrays are usedto generate highly uniform mmf over the PCB surface. As in the hexagonalembodiment described above, for convenience of illustration eachsquare-spiral winding pattern (FIG. 34) is simplified as a square symbol(FIG. 35) in the following description.

FIG. 36 shows the first layer of the square-spiral PCB winding array.The mmf in the central region of each square pattern is highest. Theseregions are highlighted as ‘Peak’ or (P) in FIG. 37. The regions of theminimum mmf (i.e., the valleys) occurs along the edges of the squarepatterns. These regions are highlighted with dots (•) in FIG. 37.

In order to reduce the mmf ripples on the surface, the peak (P)positions of a second layer of square-spiral PCB winding array canplaced over some of the valley positions (•) as shown in FIG. 38. When athird layer of square-spiral PCB winding array is added to the structurein FIG. 38, the resultant layout is shown in FIG. 39. It can now beobserved that one more layer of the square-spiral PCB windings is neededto fill up all the valleys with peaks as shown in FIG. 40.

The inductive battery charging platform described above, which can beregarded as the primary circuit of a transformer system (or the primaryinductive charging system), can be used as a standard battery chargingplatform for portable electronic equipment with compatible inbuiltsecondary circuitry in the electronic equipment to be charged. However,existing electronic equipment that is not designed for compatibilitywith the above described battery charging platform cannot take advantageof the convenience offered by the battery charging platform. Anotherembodiment of the present invention therefore provides both a batterycharging system that can stand independently and can be used to chargeexisting conventional devices, and a means by which a conventionalelectronic device can be charged using the charging platform describedabove.

Referring firstly to FIG. 41 there is shown therein a perspective viewof a part of a battery charging system according to an embodiment of thepresent invention. The part of the charging system shown in FIG. 41 maybe termed the primary inductive charging system since as will beexplained below it comprises at least one primary winding. The part ofthe battery charging system shown in FIG. 41 may also be considered tobe an extension system since in preferred forms it may be adapted tocharge multiple devices and is therefore analogous to a conventionalextension lead that allows multiple items of electronic equipment toshare the same power socket.

The charging system is provided with multiple charging slots 100,101,102for receiving secondary charging modules to be described further below.As will be explained further below each charging slot is provided with aprimary winding. FIG. 41 shows a schematic of the primary inductivecharging extension system with three charging slots. However, it shouldbe noted that the number of slots is not restricted to three and can beas few as a single charging slot, or can be more than three. It will beunderstood that the number of charging slots dictate the number ofdevices that can be charged simultaneously. The primary chargingextension system is connected to the mains through a plug 103 andincludes a power electronic circuit 104 that provides a high-frequency(typically in the range of 1 kHz to 2 MHz) AC voltage to the primarywindings that are located under the charging slot surfaces. It should benoted that the surfaces of the slots are flat and the slots areseparated from each other by dividing walls. Each slot is therefore thesame size as the surface of a housing of a secondary module to bedescribed below, and the separating walls and mechanical switches to bedescribed below together act to engage a secondary module and hold it ina correct orientation for efficient charging.

Each primary winding can be a coil 105 as shown in FIG. 42 or a printedcircuit-board (PCB) winding 106 as shown in FIG. 43. If the primarywinding is a coil 105, the coil 105 is preferably accommodated in aspace 107 defined by a magnetic structure 108 such as the two examplesshown in FIGS. 44( a) and (b) in which the coil is wound around amagnetic core 108. If a PCB winding is used, appropriate electromagnetic(EM) shielding, such as the combined use of ferrite and copper sheetsdescribed in U.S. Pat. No. 6,501,364, can be placed under the PCBwinding in order to ensure that the magnetic flux generated in the PCBwinding will not penetrate through the base of the primary inductivecharging extension system. Preferably, mechanical switches 109 can beprovided in each charging slot that when closed activate the primarywinding to the high-frequency AC voltage source when the secondarycharging module (to be described below) is inserted in that particularslot. As discussed above, the mechanical switches may also serve toengage and hold the secondary module in place. This mechanism ensuresthat only windings in the slots used by the secondary modules areexcited by the high-frequency AC voltage source. The equivalent circuitis shown in FIG. 45.

It will also be understood that the primary winding could be constructedas a multiple layer structure as discussed above in order to provide aparticularly preferred even flux distribution over the charging surface.

FIG. 46 shows a typical secondary charging module 200 for use with theprimary charging extension system shown in FIG. 41. Each secondarymodule has a conventional cable 201 and charger connector 202 that isadapted to be received within the charging socket of a conventionalelectronic device. It will be understood that different secondarycharging modules 200 may be provided differing only by the type of theconnector 202. Each secondary charging module 200 is provided with ahousing 203 that contains a secondary circuit to be described below. Thehousing is preferably rectangular (but of course could be any suitableshape) and of such a size that it may be received in one of the slots100-102 of the primary charging extension system. The housing 203 shouldhave at least one preferably flat surface for placing on the chargingslot of the primary charging extension system. This flat surface ispreferably parallel to the plane of the secondary winding within thehousing such that when the secondary module is placed in a slot of theprimary extension system the secondary winding is substantially parallelto the primary winding beneath the surface of the slot. The housing 203of the secondary module should preferably be made of non-conductive andnon-ferromagnetic material so that no current will be induced in thehousing material.

As can be seen from FIGS. 47 and 48 inside each secondary chargingmodule 200 are at least one secondary winding 204 and charger circuitry205 that receives the induced AC voltage in the secondary winding andprovides a regulated DC output voltage for the charging purpose. Thesecondary winding should be kept inside the housing. The secondarywinding can be a coil (FIG. 47) or it can be printed on a PCB (FIG. 48).The function of the secondary winding is to act as the secondary windingof a transformer system to pick up the changing magnetic flux generatedby the primary winding of the primary charging extension system.

The secondary coil or PCB winding should be placed close to the(preferably flat) surface of the housing of the secondary chargingmodule so as to pick up maximum changing AC magnetic flux from theprimary inductive charging extension system or platform. According toFaraday's Law, an AC voltage will be induced across the secondarywinding if the secondary winding senses a changing magnetic flux (thatcan be generated by the primary winding in the primary inductivecharging system).

The terminals of the secondary winding are connected to the inputterminals of an electronic circuit 205 that (1) performs the AC-DC powerconversion function (i.e., rectifying the AC voltage into DC) and (2)preferably also regulate the DC voltage to a desired value (typically inthe range from 3V to 24V) within a certain tolerance. Through a cableand a charger connector for connecting to charging socket in theportable equipment, this DC voltage can be used to charge the portableequipment as shown in FIG. 49.

The secondary winding design (such as number of turns and dimensions ofwindings), the DC regulated voltage level and the type of connector canbe designed according to the charging requirements of specificelectronic products. Therefore, different secondary charging modules canbe designed for different ranges of products, but all secondary modulesare compatible with the same primary charging extension system as shownin FIG. 50 in which two different types of secondary modules adapted forcharging different devices and having different connectors 202,202′ areshown in adjacent slots of the primary charging extension system. As theprimary inductive charging extension system preferably has severalcharging slots for accommodating the secondary charging modules, it canbe used to charge several items of conventional portable electronicequipment simultaneously.

A further advantage of the secondary charging module is that it allows aconventional electronic device to be charged using the inductive batterycharging platform described above. Although a conventional electronicdevice cannot be charged by placing it directly on the charging platformsurface because it does not have the inbuilt secondary winding, insteada secondary charging module can be placed in the inductive chargingsystem and charge the conventional device therefrom as shown in FIG. 51.

In principle, the housing of the secondary charging module can have morethan one preferably flat interface surface. If the housing is a cuboidit will have two large opposed interface surfaces (e.g., upper and lowersurfaces of a relatively thin flat cuboid structure as shown in theFigures) and with this cuboid design, either interface surface of thesecondary module housing can be placed on the charging slots of theprimary inductive charging extension system or other charging platform.This cuboid design makes the secondary charging modules veryuser-friendly because it does not matter which way up the housing of thesecondary module is placed on the primary charging surface.

In summary, a preferred embodiment of the secondary charging moduleconsists of:

a non-conductive housing that has at least one surface (and preferablytwo surfaces) for placing on the charging slot of the primary chargingextension system or the charging platform and that accommodates thesecondary winding and circuitry for charging the electronic equipment;

a secondary winding, that can either be printed in aprinted-circuit-board (PCB) or a conductor coil;

and an AC-DC power conversion circuit that converts the ac inducedvoltage picked by the secondary winding from the primary AC voltageexcitation into a regulated or unregulated DC voltage, typically in therange from 3V to 24V, a conventional cable that connects the DC voltageoutput of the secondary circuitry to a connector that is compatible withthe charging socket in the conventional electronic equipment.

It will thus be seen that, at least in preferred forms, the chargingsystem of the present invention including the proposed secondarycharging modules offers users a convenient and user-friendly batterycharging system for a wide range of portable electronic equipment. Usingthe appropriate charger connectors that are compatible with differentportable equipment, the proposed charging system enables one singlecharging system (that occupies only one power point or socket in the acmains) to charge a wide range of electronic equipment.

The present invention, at least in preferred forms, provides a newcharging system allows more than one piece of equipment to be chargedsimultaneously, and regardless of their orientations on the chargingsurface, and allows a movable device to be charged while it moves overthe charging surface.

While several aspects of the present invention have been described anddepicted herein, alternative aspects may be effected by those skilled inthe art to accomplish the same objectives. Accordingly, it is intendedby the appended claims to cover all such alternative aspects as fallwithin the true spirit and scope of the invention.

1. A charging module for a battery charging system, said modulecomprising: a charging surface for receiving a secondary module forcharging an electronic device; a plurality of transformer windingsformed in a multilayer structure comprising at least two layers, themultilayer structure positioned beneath the charging surface, each ofthe transformer windings being substantially parallel to the chargingsurface, each of the layers comprising at least one transformer winding,a transformer winding of a second of the layers being offset relative toa transformer winding of a first of the layers; and a charging circuitin a housing not including the charging surface or the multilayerstructure, the charging circuit electrically coupled to the transformerwindings.
 2. A charging module as claimed in claim 1, wherein thecharging circuit is connected to the transformer windings via a cable.3. A charging module as claimed in claim 1, wherein said chargingcircuit is integrated with an AC/DC adaptor that provides power to thecharging module from an AC power source.
 4. A charging module as claimedin claim 1, wherein the transformer windings of the first and secondlayers are offset from one another by a distance in a direction in aplane substantially parallel to the charging surface.
 5. A chargingmodule as claimed in claim 1, wherein the transformer windings of thefirst and second layers are offset such that the transformer winding ofthe second layer at least partially overlaps the transformer winding ofthe first layer.
 6. A charging module as claimed in claim 1, wherein theoffset of the transformer winding of the second layer from thetransformer winding of the first layer is such that a region of thefirst layer that generates maximum magnetic flux coincide with a regionof the second layer that generates minimum magnetic flux.
 7. A chargingmodule as claimed in claim 1, wherein the transformer windings areformed in a shape comprising at least one from the group consisting of asquare, a hexagon, a circle, a rectangle, and a polygon.
 8. A chargingmodule as claimed in claim 1, wherein the magnetic flux generated by thetransformer windings is substantially uniform over at least a majorityof the charging surface.
 9. A charging module as claimed in claim 1,wherein the charging surface is divided into a plurality of regions, andeach region is associated with a different group of one or moretransformer windings.
 10. A charging module as claimed in claim 1,wherein the transformer windings are connected to each other inparallel.
 11. A charging module as claimed in claim 1, wherein thetransformer windings are connected to each other in series.
 12. Acharging module as claimed in claim 1, wherein at least two of thetransformer windings are connected to each other in parallel, and atleast another two of the transformer windings are connected to eachother in series.
 13. A charging module as claimed in claim 1, whereinthe multilayer structure comprises at least three or more layers.
 14. Acharging module as claimed in claim 1 further comprising anelectromagnetic shield positioned beneath the multilayer structure. 15.A charging module as claimed in claim 1, wherein the electromagneticshield comprises at least two sheets of conductive material.
 16. Acharging module as claimed in claim 1, wherein when a device is placedon the charging surface, energy is transferred to the device from onlythose transformer windings located underneath the device.
 17. A chargingmodule as claimed in claim 1, wherein the charging surface is largeenough to allow two or more devices to be powered simultaneously.
 18. Acharging module as claimed in claim 1, wherein the charging module isadapted to power two or more devices simultaneously.
 19. A chargingmodule as claimed in claim 1, wherein the charging surface is largeenough to allow a device to be moved over the charging surface whilebeing powered.
 20. A charging module as claimed in claim 1, wherein thecharging module is adapted to charge a battery of a received electronicdevice.